Pressure responsive direction control valve

ABSTRACT

A hydraulic control system for a remote, double-acting piston motor in which a normally hydraulically balanced, springcentered, spool-type direction control valve is shifted from the centered position in which the opposite work ports of the motor are simultaneously pressurized to first and second positions in which fluid under pressure is selectively admitted to one or the other ends of the motor while the opposite end is exhausted. The opposite ends of the direction control valve are connected to the inlet pressures of a respective one of a pair of variable flow resistance valves and the control valve is shifted from the centered position to a selected one of the other positions by changing the resistance, hence the inlet pressure, of one of the flow valves and the control valve is returned to the centered position as a result of a feedback from the motor which shifts the other flow resistance valve until the forces on the opposite ends of the control valve are again equal.

United States Patent 3,415,163 12/1968 lnabaetal.

ABSTRACT: A hydraulic control system for a remote, double-acting pistonmotor in which a normally hydraulically balanced, spring-centered,spool-type direction control valve is shifted from the centered positionin which the opposite work ports of the motor are simultaneouslypressurized to first and second positions in which fluid under pressureis selectively admitted to one or the other ends of the motor while theopposite end is exhausted. T opposite ends of the direction controlvalve are connected to the inlet pressures of a respective one of a pairof variable flow resistance valves and the control valve is shifted fromthe centered position to a selected one of the other positions bychanging the resistance, hence the inlet pressure, of one of the flowvalves and the control valve is returned to, the centered position as aresult of a feedback from the motor which shifts the other flowresistance valve until the forces on the opposite ends of the controlvalve are again equal.

I PRESSURE RESPONSIVE DIRECTION CONTROL VALVE BACKGROUND OF THEINVENTION This invention relates to a hydraulic system for controlling aremote, double-acting motor, such as used in steering and manipulationof implement parts, and more specifically relates to a system wherein anormally hydraulically balanced, springcentercd, spool-type directioncontrol valve is provided for simultaneously pressurizing both ports ofthe motor and for selectively admitting fluid to one or the other of theports while exhausting the opposite port and wherein an input forceoperates on a variable flow resistance valve in the system for changingthe pressure on one end of the control valve to shift the control valve,and a feedback from the motor operates on another variable flowresistance valve in the system for changing the pressure on the otherend of the control valve so as to again hydraulically balance thecontrol valve.

Hydraulic systems similar to that of the invention are known, forexample in U.S. Pat. No. 2,974,639 to OConner et al. issued 14 Mar.I961. Such systems are, however, somewhat complicated and, therefore,lack hydraulic stability. Also in the known systems, no provision ismade to compensate for variances between manufactured and designdimensions.

SUMMARY OF THE INVENTION According to the present invention there isprovided a hydraulic system for controlling a remote, reversiblehydraulic motor which includes a spring-centered spool-type directioncontrol valve wherein the inlet to a first variable flow resistancevalve is connected to a fluid chamber at one end of the control valveand a second variable flow resistance valve is connected in series withthe first flow resistance valve and has its inlet connected to a fluidchamber at the other end of the control valve.

An object is to adapt one of the variable flow resistance valves forconnection to an input signal while interconnecting the output of thehydraulic motor with the other variable flow resistance valve by meansof a feedback signal.

An object of the invention is to provide a system in which the flowresistance valves may be placed remotely from each other. A

Another object is to provide normally closed adjustable flow restrictionvalves for bypassing fluid from the inlets of the flow resistance valvesfor compensating for differences in manufactured dimensions from designdimensions.

Still a further object is to provide a simplified, inexpensive 4 controlfor a two-way hydraulic cylinder which is hydraulically stable andreliable.

These and other objects will be apparent from the following detaileddescription and accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING The sole FIGURE shows a hydraulicsystem embodying the invention.

DESCRIPTION OF A PREFERRED EMBODIMENT The system includes a valve bodywhich defines a pair of similar bores 12 and 14 respectively havingclosed ends 16 and I8, and a bore 20 having first and second cylindricalportions 21 and 22 of different diameters and opposite closed ends 23and 24. The valve body 10 also defines a bore 26 which has oppositeclosed ends 28 and 30.

The bores 12 and 14 are intersected adjacent their respective closedends by inlet passages 32 and 34 respectively. The bore 12 is connectedto an outlet passage 36 spaced axially from the inlet passage 32 andleading to a sump (not shown). The inlet 32 of the bore 12 serves as anoutlet for the bore 14 and is spaced axially from the inlet passage 34.The inlet passage 34 intersects the portion 21 of the bore 20 adjacentthe closed end 23, and diametrically opposite from the intersection ofthe passage 32 with the bore 14 is a passage 37 which joins a passage 38which interconnects the inlet passage 34 and the right end of theportion 22 of the bore 20.

Also intersecting the portion 21 of the bore 20 are axially spacedsump-connected passages 40 and 42, a passage 44 midway between thepassages 40 and 42 connected to a source of fluid under pressure (notshown) and work passages 46 and 47 between the passages 40 and 44 and 42and 44 and respectively leading to the cylinder bore 26 adjacent itsrespective closed ends 28 and 30. A passage 48 interconnects the passage44 and the inlet passage 32 and contains a manually preset restriction49 which may be an adjustable needle valve.

The bores 12 and I4 respectively carry variable flow resistance valves50 and 52. The flow resistance valves 50 and 52 respectively havereduced piston portions 54 and 56, which bridge the respective outletpassages 36 and 32 of the bores 12 and 14, and piston rods 58 and 60extending respectively through the bore ends 16 and 18. O-ring seals 62and 64 respectively encircle the other ends of the pistons 54 and 56.

A pressure responsive control valve 66 is axially movable in the bore 20and includes leftand right-hand pistons 68 and 70 respectively slidablyfitting bore portions 21 and 22. The purpose of the enlarged boreportion 22 and piston 70 will be explained below. The control valve 66further includes a pair of axially spaced lands 72 and 74 respectivelyat the leftand right-hand sides of the passage 44. Springs 76 and 78 arerespectively positioned between the opposite ends 23 and 24 of the bore20 and the oppositely directed faces of the pistons 68 and 70 andnormally center the control valve 66 at the position illustrated whereinthe lands 72 and 74 respectively block the passages 42 and 44. A screwelement 79 combines with the spring 78 for adjusting the centeredposition of the valve 26.

The cylinder bore 26 carries a piston 80 having oppositely extendingpiston rods 82 and 84 which respectively extend through the bore ends 28and 30. A feedback 86, here shown as mechanical, moves the flowresistance valve 52 in response to movement of the piston 80 andincludes a lever 88 fulcrumed at 90 intermediate its ends and havinglost motion connections 92 and 94 at opposite ends connectedrespectively to the piston rods 60 and 82. While the inputandfeedbackconnected valves 50 and 52 respectively are shown in a commonvalve block, it is significant that they may be mounted remotely fromeach other.

In order to compensate for any difference in the dimensions of themanufactured device from the design dimensions, which would causeundesired flow to the flow resistance valves 50 and 52, a bypass 96 tothe sump is provided in the inlet passage 32 and contains a manuallyadjustable restriction 98 and a similarly manually adjustablerestriction 100 is located in the passage 38 adjacent to the inletpassage 34 for bypassing fluid from the passage 34 to the passage 38.

The operation of the system is described here as applied to powersteering. In such application, the piston rod 58 of the flow resistancevalve 50 would be connected to receive steering wheel movement formoving the flow resistance valve in the bore 12. The restriction 49 isadjusted to insure the provision of enough fluid to operate thehydraulic motor and to adequately supply flow to the flow resistancevalves 52 and 54. Although the preferred embodiment shows connections toa single source of fluid pressure, it should be understood that separatesources may be used for the flow resistance valves and hydraulic motorand the fluid for valve operation need not be hydraulic fluid.

Assuming that the steering gear of the vehicle is positioned forstraight ahead travel, the hydraulic system will be in the equilibriumcondition illustrated wherein the flow restriction valves 50 and 52occupy positions with respect to the respective outlet passages 36 and32 which establish a preselected ratio of pressure drops correspondingto a preselected ratio of the distance the piston portion 54 extendsupstream from the outlet 36 as compared to the distance the pistonportion 56 extends upstream from the outlet 32, and the control fluidpressures existing in the passages 34 and 38 respectively wiil. inconjunction with the pressure existing in the sump-connected passages 40and 42, exert equal and opposite forces on the smaller diameter piston68 and the larger diameter piston 7Q.

The pressure-responsive control valve 66 is thus hydraulically balancedand is centered by the springs 76 and 78. In this position the lands 72and 74 block the respective passages 46 and 47.

If it is desired to steer the vehicle to one side or the other, thesteering wheel is merely turned so as to shift the flow resistance valve50 either to the left or right from the position illustratcd. Assumingthat the valve 50 is shifted to the right, the left end of the piston 54will move closer to the outlet passage 36, and the resistance to fluidflow from the passage 32 to the sump passage 36 will be decreased. Witha decrease in resistance to flow, the pressure of the fluid in thepassage 32 will correspondingly decrease and this decrease in fluidpressure will occur in the passage 38 and result in a lesser force beingapplied to the larger piston 70 of the control valve 66. Since theforces on the opposite end of the control valve are no longer equal, thecontrol valve will shift to the right and connect the passages 46 and 47respectively to the sump passage 40 and to the pressure passage 44.Since the right end of the hydraulic motor cylinder 26 is nowpressurized, the piston 80 will shift to the left to turn the wheelbeing steered and simultaneously cause the feedback lever 88 to pivotclockwise and shift the restriction valve 52 to the right until thepressure in the inlet passage 34 decreases enough to again balance theforce exerted by fluid pressure on the opposite ends of the controlvalve 66, allowing the compression springs to again center the controlvalve whereby the hydraulic motor will be held in its shifted position.The design of the system is such that the position that the left end ofthe piston 56 of the flow resistance valve 52 now occupies with respectto the outlet 32 as compared to the position occupied by the piston 54of the flow resistance valve 50 with respect to the outlet passage 36will be the ratio preselected. Also, the preselected ratio of pressuredrops will again be established.

An operation similar to that described above when shifting the flowresistance valve 50 to the right will occur if the flow resistance valveis shifted to the left from the position illustrated, but the directionsof movement will of course be reversed. That is to say, pressure willincrease in the passage 38 and the control valve 66 will shift to theright. In this position of the control valve, fluid under pressure isconnected to the left end of the cylinder 26 and the right end isconnected to sump; thus the piston 80 will shift to the right and pivotthe lever 88 counterclockwise to shift the flow resistance valve 52 tothe left until fluid forces on the opposite ends of the control valve 66are again equalized and the control valve is moved by the compressionsprings to the centered position.

In the event that the manufactured dimensions of the various bores andpassages differ from the designed values for a preselected flow, theflow into the bores and passages, and, hence the pressures, may beadjusted by opening the normally closed restriction valves 98 and 100 tobypass such fluid as is necessary to achieve pressures at the oppositeends of the control valve 66 to apply equal forces to its opposite endsfor a preselected position of the flow resistance valves 50 and 52.

it should be understood that the hydraulic system may be used forapplications other than power steering, for example, for adjusting andholding an agricultural implement at a selected working position. Insuch an application, the piston rod 58 of the flow resistance valve 50would be attached to a means which would follow the contour of theground s surface while the piston rod 78 of the hydraulic actuator wouldextend between the implement and the support frame to hold the implementa preselected distance relative to the surface of the ground and wouldbe automatically actuated to raise and lower the implement to compensatefor variations in ground contour.

lclaim:

l. A hydraulic system comprising: a control conduit means includingvariable flow resistance means for establishing control pressures atfirst and second series connected locations, a valve bore means, conduitmeans for connecting a source of fluid under pressure to said controlconduit means upstream from said first location and to said valve boremeans, return fluid passage means intersecting said valve bore means, areversible hydraulic motor having a pair of work passages connected tosaid valve bore means, a control valve means axially shiftable in saidvalve bore means between a neutral position wherein fluid is blocked tothe work passages of the hydraulic motor and active positions whereinone or the other of the work passages is connected to fluid pressurewhile the opposite work passage is connected to the return passagemeans, bias means normally holding said control valve means in saidneutral position, said control valve means including means for sensingthe control pressures at said first and second locations and fordirecting forces represented by the pressures in opposite axialdirections, means for adjusting said variable flow resistance means to apreselected position for causing a ratio of control pressures which willresult in equal and opposite forces being applied to said control valvewhereby said bias means will hold said control valve in said neutralposition, said flow resistance means being adapted for connection to aninput signal for disturbing the preselected ratio of control pressuresso that the control valve means will shift to one of said activepositions to cause actuation of said hydraulic motor, and feedback meansinterconnecting the output of said motor with said flow resistance meansfor adjusting the latter for reestablishing the preselected controlpressure ratio whereby the bias means will again return the controlvalve means to its neutral position.

2. The invention defined in claim 1 wherein the variable flow resistancemeans comprises first and second valve bores respectively at said firstand second series connected locations, each of said valve bores havingan inlet and an outlet, the series connection between the locationsbeing between the outlet of the first bore and the inlet of the secondbore, first and second pistons being of lesser diameters than said firstand second bores, respectively, and being positioned for axial movementin at least the portions of the bores between the respective inlets andoutlets for causing a variable pressure drop between the respectiveinlets and outlets, and one of said pistons being adapted for connectionto said input signal and the other of said pistons being connected tosaid feedback means.

3. The invention defined in claim 1, said control conduit means furtherincluding adjustable means for bypassing selected amounts of fluidaround said first and second locations for aiding in establishing saidpreselected ratio of pressure drops.

4. The invention defined in claim 2, said control conduit means furtherincluding adjustable means for bypassing selected amounts of fluidaround said first and second pistons for aiding in establishing saidpreselected ratio of pressure drops.

5. The invention defined in claim 1 wherein the means for sensing thepressure drops includes piston means.

6. The invention defined in claim 5 wherein the valve bore meansincludes first and second portions, the first portion being of a smallerdiameter than the second, said piston means comprising first and secondpistons positioned respectively in and being of diameter sufficient tospan said first and second bore portions, said control conduit meansconnecting the inlet of said first bore to one side of the smallerpiston for exerting a force in one axial direction and connecting theinlet of said second bore to one side of the larger piston for exertinga force in the other axial direction.

7. A hydraulic system comprising: a valve bore, supply and returnconduit means intersecting said valve bore, a reversible hydraulic motorhaving a pair of work passages, a pressure responsive control valvemeans positioned in said valve bore for axial shifting movement from anormally maintained neutral position wherein said work passages of themotor are blocked to either of two active positions wherein said supplyconduit means is connected with one or the other of said work passagesof said motor while simultaneously interconnecting the opposite workpassage with said return conduit means,

bias means tending to maintain said control valve means in said neutralposition, control conduit means being adapted for connection to a sourceof fluid under pressure and including first and second series connectedflow resistance valve means, each having an inlet connected to saidcontrol valve means so as to normally apply equal and opposite actingforces on the control valve whereby said bias means maintains saidcontrol valve means in said first position, one of said flow resistancevalve means being adapted for connection to and being responsive to aninput signal for selectively causing changes in pressure at its inletfor causing an unbalance of said oppositely acting forces on saidcontrol valve thereby causing the control valve to shift axially to oneof said active positions for operating said hydraulic motor and afeedback means interconnecting the output of said hydraulic motor andthe other of said flow resistance valve means for causing adjustment ofsaid other flow resistance valve means for creating a pressure at itsinlet for again producing an equal and opposite force on said controlvalve means whereby the bias means will again restore said control valvemeans to said neutral position.

8. The invention defined in claim 7 wherein said flow resistance valvemeans includes first and second bores each being intersected by an inletand an outlet port, conduit means interconnecting the outlet port ofsaid first bore with the inlet port of said second bore, said controlvalve means including pistons at its opposite ends, said control conduitmeans further including first and second conduits respectivelyinterconnecting the inlet ports of said first and second bores with oneof the opposed faces of said pistons, said pair of flow resistance valvemeans each being positioned in a respective one of said bores andincluding an axially shiftable piston portion of lesser diameter thanthe bore bridging the outlet port and having one end positioned betweenthe inlet and outlet ports and a fluidtight seal annularly disposedabout the other end and means for connecting the piston portion of oneof said flow resistance valves to said input signal means and saidfeedback means being connected to the piston portion of the other ofsaid flow resistance valves.

9. The invention defined in claim 8 and further including a normallyclosed adjustable restrictor valve interconnecting said first and secondconduits, and said conduit means connecting the outlet port of saidfirst bore with the inlet port of said second bore also including anadjustablenormally closed restrictor valve joining the conduit meanswith the sump, whereby said restrictor valves may be opened to bypassfluid for adjusting the pressure in the first and second conduits.

1. A hydraulic system comprising: a control conduit means includingvariable flow resistance means for establishing control pressures atfirst and second series connected locations, a valve bore means, conduitmeans for connecting a source of fluid under pressure to said controlconduit means upstream from said first location and to said valve boremeans, return fluid passage means intersecting said valve bore means, areversible hydraulic motor having a pair of work passages connected tosaid valve bore means, a control valve means axially shiftable in saidvalve bore means between a neutral position wherein fluid is blocked tothe work passages of the hydraulic motor and active positions whereinone or the other of the work passages is connected to fluid pressurewhile the opposite work passage is connected to the return passagemeans, bias means normally holding said control valve means in saidneutral position, said control valve means including means for sensingthe control pressures at said first and second locations and fordirecting forces represented by the pressures in opposite axialdirections, means for adjusting said variable flow resistance means to apreselected position for causing a ratio of control pressures which willresult in equal and opposite forces being applied to said control valvewhereby said bias means will hold said control valve in said neutralposition, said flow resistance means being adapted for connection to aninput signal for disturbing the preselected ratio of control pressuresso that the control valve means will shift to one of said activepositions to cause actuation of said hydraulic motor, and feedback meansinterconnecting the output of said motor with said flow resistance meansfor adjusting the latter for reestablishing the preselected controlpressure ratio whereby the bias means will again return the controlvalve means to its neutral position.
 2. The invention defined in claim 1wherein the variable flow resistance means comprises first and secondvalve bores respectively at said first and second series connectedlocations, each of said valve bores having an inlet and an outlet, theseries connection between the locations being between the outlet of thefirsT bore and the inlet of the second bore, first and second pistonsbeing of lesser diameters than said first and second bores,respectively, and being positioned for axial movement in at least theportions of the bores between the respective inlets and outlets forcausing a variable pressure drop between the respective inlets andoutlets, and one of said pistons being adapted for connection to saidinput signal and the other of said pistons being connected to saidfeedback means.
 3. The invention defined in claim 1, said controlconduit means further including adjustable means for bypassing selectedamounts of fluid around said first and second locations for aiding inestablishing said preselected ratio of pressure drops.
 4. The inventiondefined in claim 2, said control conduit means further includingadjustable means for bypassing selected amounts of fluid around saidfirst and second pistons for aiding in establishing said preselectedratio of pressure drops.
 5. The invention defined in claim 1 wherein themeans for sensing the pressure drops includes piston means.
 6. Theinvention defined in claim 5 wherein the valve bore means includes firstand second portions, the first portion being of a smaller diameter thanthe second, said piston means comprising first and second pistonspositioned respectively in and being of diameter sufficient to span saidfirst and second bore portions, said control conduit means connectingthe inlet of said first bore to one side of the smaller piston forexerting a force in one axial direction and connecting the inlet of saidsecond bore to one side of the larger piston for exerting a force in theother axial direction.
 7. A hydraulic system comprising: a valve bore,supply and return conduit means intersecting said valve bore, areversible hydraulic motor having a pair of work passages, a pressureresponsive control valve means positioned in said valve bore for axialshifting movement from a normally maintained neutral position whereinsaid work passages of the motor are blocked to either of two activepositions wherein said supply conduit means is connected with one or theother of said work passages of said motor while simultaneouslyinterconnecting the opposite work passage with said return conduitmeans, bias means tending to maintain said control valve means in saidneutral position, control conduit means being adapted for connection toa source of fluid under pressure and including first and second seriesconnected flow resistance valve means, each having an inlet connected tosaid control valve means so as to normally apply equal and oppositeacting forces on the control valve whereby said bias means maintainssaid control valve means in said first position, one of said flowresistance valve means being adapted for connection to and beingresponsive to an input signal for selectively causing changes inpressure at its inlet for causing an unbalance of said oppositely actingforces on said control valve thereby causing the control valve to shiftaxially to one of said active positions for operating said hydraulicmotor and a feedback means interconnecting the output of said hydraulicmotor and the other of said flow resistance valve means for causingadjustment of said other flow resistance valve means for creating apressure at its inlet for again producing an equal and opposite force onsaid control valve means whereby the bias means will again restore saidcontrol valve means to said neutral position.
 8. The invention definedin claim 7 wherein said flow resistance valve means includes first andsecond bores each being intersected by an inlet and an outlet port,conduit means interconnecting the outlet port of said first bore withthe inlet port of said second bore, said control valve means includingpistons at its opposite ends, said control conduit means furtherincluding first and second conduits respectively interconnecting theinlet ports of said first and second bores with one of the opposed facesof said pistons, sAid pair of flow resistance valve means each beingpositioned in a respective one of said bores and including an axiallyshiftable piston portion of lesser diameter than the bore bridging theoutlet port and having one end positioned between the inlet and outletports and a fluidtight seal annularly disposed about the other end andmeans for connecting the piston portion of one of said flow resistancevalves to said input signal means and said feedback means beingconnected to the piston portion of the other of said flow resistancevalves.
 9. The invention defined in claim 8 and further including anormally closed adjustable restrictor valve interconnecting said firstand second conduits, and said conduit means connecting the outlet portof said first bore with the inlet port of said second bore alsoincluding an adjustable normally closed restrictor valve joining theconduit means with the sump, whereby said restrictor valves may beopened to bypass fluid for adjusting the pressure in the first andsecond conduits.